Im really not sure if you can other than by making the pics smaller in export settings as you mentioned… (in quality not size..)

Are the pics .jpg when you place them into the document? for example if you use In design to build the document, the original linked images should be saved as the same physical size in Photoshop that they appear in the document and as an RGB jpg. Rather than placing them and then re-sizing them within the page layour. That may make a difference… otherwise split into 2 files..? That is assuming you dont need it to be printed offset at high res (in which case you’d have to create  2 files)

Id be interested to hear any other way.