If you are copying and pasting, the picture size is not cut in half, it is only scaled down.
Using MSWord, all pictures you put into the document will add to the file size of the word document. You state your pictures are average of 1.5 mb. That means, without actually editing, resizing, and resaving the images before using them in MSWord, if you for example, put 10 images in the word doc, you doc will be at least 1.5x10 mb in size. Now you are looking at a 15 mb word document.
A MUCH better way for adding images to Word would be to open the images in some editing software. Gimp for a photoshop type program or IrfanView for an easier to learn editor are both completely free to download. For simplicity, I would recommend Irfanview. I don't know the exact steps and menus, but it is something like this... Open the image, go to the "Edit" menu (I'm guessing here) and select "Resize". Resize the image at least down to 800x600. Even that is a very large file (too large to fit in Word without further scaling from within Word). Resave that file with a different file name to be sure the original is untouched (Resave as filename-copy.jpg for example.)
Now, within Word, in the Insert menu you will see "Picture" and another dropdown box will appear and you will see "From file..." Select that, navigate to where you saved the resized image and select that. It will help to keep your Word doc from becoming gigantic.
You can then scale the images down a bit from within Word by double clicking the image, selecting the "Size" tab, and scaling it down with a percentage from there.