An image at that size for print-quality would be rather beefy in file size just to start. (I would make sure that Photoshop's the only thing running. Close Bridge and anything else unneeded in the background.) Adding RAW images complicates it further.
When you say you adjust size of the photo, are you resizing up or down? How many images are there?
Also, how are you printing this? I'm assuming you're vending it. Check with the printer to find out the resolution of the file you should be using. For a large mural, you may not need a high dpi setting. For example, most prints at 8X10 inches are good at 300dpi, but when I make a 30X40 I cut the dpi down to 150, other wise the printer bogs down, and you really don't see the cut in dpi at that size. So you might be taxing your system trying to make it too high of a resolution. Having the high resolution will not help you if you are enlarging low res images.
Thanks for the reply
When I say adjust the image, I mean blowing them up. The wall is 101'' by 106''. There are about 20 19mp pictures, blown up to all different sizes. They are overlapping in certain spots. To give you an idea of what it looks like ill attach a screen shot. I was just talking to the printer, and he seems confident that this will look great. Also, thanks for the explanation about he DPI. What I was doing was zooming to 100 percent. I thought that this would be what size the pixels would be at print size. Instead I found that if I turn on rulers and zoom until the rulers show inches I will see the true print size. This looks much better then what I had.
I see two problem. On the print size exceed all the printers I know of. The widest printers that Epson make can only print 64" wide. Even if you cut your collage into two with some overlap for alignment. It would be a nightmare applying 54" wide wallpaper to a wall. There might be a third problem with cost a Epson printers that can print 54" wide rolls starting price is $10,000.00 and go up to $25,000.00. Expensive wallpaper. And you still need the paper and ink.
For a collage that large you do not need to print at 300 DPI for you will not be viewing the wall that is big and over your height up close where the human eye can resolve down to 300 dpi. In you collage you also show only three image across the top row. Some wider the others. Look at your Cannot T4I the would mean some image would be printed between 35" to 40" wide. without interpolation your 18MP images printed that size would meant they would print in the 130 to 150 DPI range. To interpolate from 130-150 to 300 would requite increasing the pixel count in the range of 400 to 500 percent. That is a lot of interpolation. I would not do that. I would actually create the collage at 150 DPI. That resolution should be good for an image that large. That Collage would not tax Photoshop as much. The 300DPI collage image would be 106x300x101x300=963,540,000 at 150DPI the same image would be 106x150x101x150=.240,885,000 the is 1/4 the number of pixels.
I would flatten the collage and cut it into 7 ovelaping stripts around 16" wide
Thanks for the tips
I was able to find a printer that has a printer that can print this out on one piece of material. They print stuff for Nascar and other large corporations. And this will be put on a wall in a small room, so people will be looking at it from up close. The printing company will take all of that into account when they go to print it.
I will use the tips on the DPI in later projects, it was a nightmare creating this at 300dpi.