Is there a chance to tune the performance of this extension somehow on a server that neither allows for APC nor for memcached. What I have done is to activate $wgUseFileCache but his one has basically a different scope so this did not help much if at all. Probably the best recommendation will be to upload just files in webquality as jpeg or gif (100 - 250 KB) rather than in full quality (1 MB+)?
Topic on Extension talk:MultimediaViewer
$wgUseFileCache is about page caching. You probably want $wgMainCacheType = CACHE_DB; although this depends on what exactly is slow (maybe you could profile it?). FWIW image transformations are cached by storing the thumbnails, so that should not be affected by lack of memcached/APC.
(Personally, I would just switch hosts. Running a site without an opcode cache is a bit masochistic.)
Thanks a bunch for your help and suggestion. Yeah, you are right with your assessment about the host and I totally agree, but reality prevents changes in this respect. So ...
I set the main cache type to CACHE_ANYTHING which is basically the same as CACHE_DB in this case.
A performance issue was Vector's JavaScript, but there was actually a much bigger worry: browser caching and content compression were not enabled. :( I believe thing should be much better now.