Quote Originally Posted by Carnifex
I am pretty sure you can work in 150 dpi or lower.
I seriously can't, I have no choice here. 300dpi is a guideline here, I can't change that.

Thank you all, the issue has now been resolved. I gut a new Windows-PC paid by the company I work for now full time from home office, that is really high-end - now at home. 4,0 GHz, 32GB RAM, 500GB-SSD, etc. is probably the best you get for a reasonable price. I think it will force me to split them up in 4 parts, but at least it won't be a huge pain to work on it. I think I will try some of your suggestions and let you know which of them worked for me, maybe I even make another tutorial. We'll see! =)

Thank you guys so much!
Steffen