I am a monthly subscriber to the Adobe PS and LR and my system info is below.
My problem is that the Develop module frequently crashes and becomes unresponsive shortly after starting to use it. The image last used stays on screen - I can go to the Library module and the hightlighted image will change in the navigator but sticks in the Develop module...
My full catalogue is big (it warns me that it is over 4GB) and contains about 30000 images - mostly RAW
I have to close down LR and start it up again to get it to work .
Any help would be appreciated
PS - I HAVE THE GRAPHICS CARD UNTICKED IN THE PREFERENCES.PERFORMANCE
Lightroom version: CC 2015.8 [ 1099473 ]
License: Creative Cloud
Operating system: Mac OS 10
Version: 10.10 
Application architecture: x64
Logical processor count: 4
Processor speed: 2.7 GHz
Built-in memory: 12,288.0 MB
Real memory available to Lightroom: 12,288.0 MB
Real memory used by Lightroom: 1,439.5 MB (11.7%)
Virtual memory used by Lightroom: 2,948.6 MB
Memory cache size: 693.3 MB
Maximum thread count used by Camera Raw: 4
Camera Raw SIMD optimization: SSE2,AVX
Displays: 1) 2560x1440
Graphics Processor Info:
AMD Radeon HD 6770M OpenGL Engine
Check OpenGL support: Passed
Vendor: ATI Technologies Inc.
Version: 4.1 ATI-1.32.25
Renderer: AMD Radeon HD 6770M OpenGL Engine
Application folder: /Applications/Adobe Lightroom
Library Path: /Users/Joy/Pictures/PhotosHOME/HOME PHOTOS/HOME PHOTOS-2-2-2.lrcat
Settings Folder: /Users/Joy/Library/Application Support/Adobe/Lightroom
That 4GB error can be ignored. Just click the Don't show this again (or something like that) check box.
You are probably deleting images while in the Develop module. Go back to the Library module to Delete images. Pressing the e or g keys will take you back to the Library module, Loupe or Grid view respectively. Or once you X images for deletion move off the X'ed images before you delete.