when I submit an image to WP media gallery or trough various plugins, the process takes quite some time to complete.

A 4MB image takes like 2-5 seconds to upload (got fast connection), then there is like 20 seconds processing before the process complets. So if I upload several images i reach minutes of waiting territory which is quite annoying.

I noticed for each image 12 size variations are created: 3 WP defaults, 5 from the SELA theme, and I don't know from where the others are ordered. Is this the cause of the problem? Would removing image size creation help?