A possible way round this could be instead of embedding the picture files in the presentation, link them to files on the (or a ) hard drive.

You do this by the usual "Insert>Picture>FromFile> and then tick Link to File

Or
Split your presentation into more manageable sizes, maybe 10 slides at a time (or by whatever structure suits the presentation) so you don't have to work with the whole thing.

?

When 40 mins loading(!!!!) is the base file on the local drive or on a newtork store? From local it does seem a silly amount of time!

Let us know if any progress!

Good Luck!