To Reproduce:

1. Open the attached project and Play.
2. Click 'Test 2'
3. Wait until the test is completed and click 'Test 2'
4. Unity crashes with an out of Memory error

Seems that memory isn't fully cleared after calling DestroyImmediate, if it's called after creating each texture, after running the test Textures use ~7mb, but mono still uses up around 1.2GB of memory which is never released (after running Test 2 once).

Memory usage after running 'Test 2' once in editor:

4.5.1p5: 1.47GB
5.0.0b21: 350MB