as stated above I'm working on a Macbook Pro 13" (late 2008) with 4 GB of memory. My system is a OS X 10.10.5 (14F1509).
My Blender is a 2.75a., but I see the same issue with other Blender versions.
Same behavior on a Intel i5 Windows 7 machine with 32GB and Blender 2.76b.
Short description of error
I'm working with quite large files which have been created by exporting an stp from CATIA, conversion to 3DS with Glovius and importing to Blender. The so created Blender file I am currently working with has a size of roughly 290 MB. A typical error in the conversion process is that the objects created thereby have many duplicate vertices, but this seems not to be the reason for the behavior I see.
When working with the file (typical operations consist of joining objects, moving objects to levels and cleaning the duplicate vertices) the operations work sufficiently smoothly and with satisfactory performance. After a couple of operations the program gets increasingly slower and after something like 5-6 operations each click results in waiting times of up to several minutes.
The only way to work with these kind of large files is to save often to kill Blender when it ran into the slow mode and to open the file again. Even is the operation was slow before killing Blender, the same operation is normally fast after opening the file again. I see this behavior with every file above a certain file size - can't exactly tell which size. If I decrease the file size by removing duplicate vertices, deleting objects, etc. and the size gets below the threshold, the performance goes back to normal.
Exact steps for others to reproduce the error
Work with the attached file: select objects and jin them, remove materials, mode objects to layers, remove duplicate vertices, etc.