The memory limit only blocks PHP from allocating more than that amount of memory for a single process (i.e. client request). Given that you're barely scratching the surface of your 2GB of memory, if you don't expect too many 17MB file uploads to happen at the same time from different users, you should be okay.
If you get a lot of large file uploads in clusters, you may end up rejecting requests from clients trying to upload small files. I suppose this isn't much worse than rejecting all large file uploads, and will stop happening once those large files are completed. David