Salut denost2!
When unpacking your age files, I saw that your textures PRP is REALLY LARGE. About 180 MB (!), the largest I've ever seen.
Because I became interested in how this is caused, I had a closer look into the PRP with PrpShop - and I found that many of your textures are included in the file as duplicates.
For example, the texture called "Bois_entrelac_Seamles" is stored FIVE TIMES in the file, although it's always the same.
1. Bois_entrelac_Seamles
2. Bois_entrelac_Sea
3. Bois_entrelac_Sea.001
4. Bois_entrelac_Sea.002
5. Bois_entrelac_Sea.003
And there are textures which are stored 15 times (!) in the file, e.g. "RustLeak_M.jpg", just with various names, but same content. And this matters, because it's a 1024x1024 texture.
You should avoid this.
It is caused by Blender, when you assign a texture to an object, e.g. when you load an already used texture again instead of choosing it from the list of already loaded ones.
You can see that this happend when you check the name of the texture. So when a texture is called Bois_entrelac_Sea.001 instead of Bois_entrelac_Sea, this texture is NOT SHARED or re-used, but in fact stored as a different texture.
And during export, this texture is exported as a different texture as well, and not re-used.
Actually this makes your texture PRP about 3-5 times larger than needed.
If you want to correct this, you should have a look into each texture assignment and change them to point always to the *same* texture name.
E.g. make each material that uses the image "Bois_entrelac_Sea" point to exactly this name, not to "Bois_entrelac_Sea.001" or others.
If you're unsure how to do this in detail, just ask.
(I hope I described it in a way you understand).
I cannot predict how much this reduces lag, but it will definitely reduce load time a lot.
Finally, this is going to become a really nice age.

(Currently I have much lag as well, and I don't have a slow computer. Not the fasted available today, but it was fast enough to be able to win the Pellet Run Contest in MOUL some while ago, where I player the "Runner", at screen resolution 1920x1200, and we won the medal. Hehe. Just to give you an idea about what to expect to be "average" PC speeds.)
Bonne nuit,
tach