1) If you want to keep your file editable and simply make the document less heavy to modify:
You're saying your images are embedded and in tiff format. I know it's time consuming but only changing the file format to something else would help a lot and might not require any resizing.
You can open the "links" window, and select the image, and then click on the small "option" panel of the "links" panel... and select "unembed".
A window will open and prompt you to save the image in psd. You can do this for each image. Once you're done, you can freely modify the resolution and file format, and keep these images linked instead of being embedded. This will greatly improve the performance of your Illustrator.
But don't forget to provide these linked images to your printer or embed them again before sharing this file!
2) If you only need to make texts changes and don't mind losing the ability to move the images around:
You can save your Illustrator file as a PDF, and optimize the file in Acrobat Pro (Save as other/optimized PDF) and compress all your images to 300 or 600 dpi, to your preference. Then open your PDF file again in Illustrator.
Personally I don't like method much because it crops the images too and merge some elements together. It's then harder to edit the file.
Another thing you can do since you don't want to unembed the images: You could select the images and rasterize a few together. To do this, simply select them together and use the command "rasterize" in the "object" menu. You'll be able to also "equalize" the resolution at this point but you'll lose the ability to modify individually each image.
You can also rasterize every image individually if your issue is the resolution of some images being too high for what you need. It's a bit faster than doing it in Photoshop and updating your linked images.
