Users are noting higher CPU usage on builds in the 5.3 versus 5.2.3. Here are some screens from the profiler:
5.2.3
5.3
Same scene from the exact same camera angle. (Lights were rebaked for 5.3)
5.2
5.3
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Okay set Unity 5.3 back to OpenGL 2.1 and now the profiler looks like this:
This is on OSX, but users on Windows are reporting worse performance overall. Their defaults seem to be Direct3d9.
I’m getting a very bad performance as well with OpenGL 4.1 profile on the latest El Capitan:
I’m running this on a late 2012 quad core iMac with GeForce GTX 680MX.
This gets fixed if I switch back to the old OpenGL profile.
Hmm this is really interesting! Thank you so much for posting! I’m going to send this forum thread over to the WebGL team 
Note: These are native OSX64 and Windows 64 version that are receiving worse performance. Not sure if WebGL affects?
Oh gosh! I totally mis-read! Thank you so much! I’ve posted to the graphics team
On iOS, the same game scene now has doubled CPU time per frame after updating to 5.3, which caused frame rate to drop by 1~4 fps. I used dozens of particle systems but it was 60 fps smooth in 5.2.3p2.
It could be one of the new particle features that create the issue, i hope this will be addressed swiftly.
I read particles have some new shadowing features too, maybe these are heavy and are enabled by default ?
Same problem, changing the editor back to opengl 2.1 solves the issue for me.
On a 2015 Macbook Pro (dual core 3,1 GHz Intel Core i7 + Intel Iris Graphics 6100) this problem does not manifest itself. What’s going on? 
I tested a bit more, some times the particles work ok, others they have some very bad spikes and hangs that never appeared before in previous versions. Another guess is that the new threading system bottlenecks and maybe it increases speed temporarily, but create a hang at random (which is what i experience)
That’s probably the cause. Looking forward to p1.
I actually found some of the profiler differences in the original post to be of interest:
Used Textures
5.2 - 109 - 238.4 MB
5.3 - 0 - 0 B
VRAM usage
5.2 - 48.2 MB to 328.6 MB
5.3 - 48.2 MB to 90.1 MB
There were slight differences in draw calls and batching and a fairly significant difference in SetPass calls (going from 1015 to 731). It’s possible that the profiler isn’t returning the proper information for OpenGL 4.1 in Unity 5.3. It does look like these differences should be favorable for 5.3, yet it performs slower on the CPU side.
I’m also getting awful performance on OSX builds (about -50%) with OpenGL 4.1. Anyone from Unity know why?
I have a project that I’m using to test vertex/poly limits that was running on a particular Android device at 30fps using Unity 5.2.3f1. After upgrading to Unity 5.3, that frame rate has dropped to 7fps. I cannot attach the profiler on Unity 5.3 as doing so immediately crashes the application for memory (this is not the case on 5.2.3f1). Whatever is going on seems to be across multiple platforms.
I’ve got also awful performances on Android builds.
I tested with a scene with a bunch of meshes.
Some of them usign a particule additive shadder
near 200ms just for the transparent rendering in profiler ! 4fps !!
The same scene was 60fps stable on 5.2 on the same targeted device just before upgrading.
Any idea why ? I am really interested by some features of 5.3, but for now, I will roll back 
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Using a 27" 2013 iMac 2.5ghz i7 8Gig ram. OSX 10.10.5.
In editor and builds the FPS is capped to 30. It used to be between 30-60 in editor and a rock solid 60FPS in builds.
There must be a bottleneck somewhere that’s causing this 30FPS limit.
Because of the low FPS, if I apply any kind of post-process/image effect it drops to 15FPS. Regardless of which one I pick. I appreciate post process is expensive, but it shouldn’t be a universal 50% hit.
@holliebuckets_1 or someone in Unity : can you please confirm this bug and/or suggest further tests?
*Edit: not certain if this helps :
- I had to disable AA for ‘Beautiful’ and ‘Fantastic’ as it made everything washed out. So something is going wrong there
- Builds run just fine on Windows
- Seems to run just fine on a newer OSX 10.11 5k iMac (2014, i7, 24 gig of ram).
- Shrinking the editor window to something tiny (200x200 ish) makes the FPS to go over 45. So probably not a hard cap… Just awful performance on this machine.
Let me know when i can upgrade from 5.1.2f (stable and fast) to new that are infact better and not just new functions .
5.2 and 5.3 seams like beta, and not very well tested. UI low performace…both this version… Fix it please…
Submit bug reports, please…
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Are you serious? It’s hard to create a simple default scene to test the engine?
Check that http://forum.unity3d.com/threads/performance-issue-after-5-1-3.373038/