New GM. Will a 80x105 map slow the game down because of its size?

So I’m DM:ing through my first campaign (Lost mine of Phandelver) and my group is closing in on the final dungeon, which means I need to prep it. I plan on putting out all tokens in advance, and also write and draw some reminders to myself in the GM info layer. We do not play with dynamic lightning or advanced fog of war, but the players enjoy the 3d dice (I DM without it). Will such a big dungeon cause lag, and will I be better of splitting up the map into different parts? If so, is there an easy guide how I can do this (been messing around with Gimp, but I find the program hard to use and not very intuitive)? We have been experiencing some lag already with maps the size of 40x30, but nothing that have been too bad (just wait a bit for dice rolls to show). I do not want to have to cancel a playing session and redo the whole thing, so advice based on your knowledge and experience is very appreciated.

I regularly use maps that large (larger even, with dynamic lighting no less) and it seems to work OK for my group.  The initial load can take a bit, but once loaded it seems OK.

There are a lot of variables. You will probably see better performance if you split your map up into 4-6 parts and fit them together in Roll20. It's then serving more manageable chunks of graphics than a monolithic piece. Make sure your maps are jpg, not png, and you don't go nuts with the DL (probably avoid AFoW on a map that size, and if you do use it, avoid Global Illumination).

Thankyou. I didn't manage to split the map into segments so I'm going to use it in full size. 

Be careful if some of your players are on a metered connection, some images can get quite big, and as far as I can understand roll20 pulls the full size image, then resizes it. Other than that, lag is only while loading the game. If some of your players have abysmal connections just tell them to start loading half an hour before the start and leave the browser window open.

I think Roll20 generates and serves some different resolutions, to speed display, but I could be wrong.