New SIM card from another country for iPhone?

This summer, I'm going on holiday and in my iPhone 6 I'm going to put a new SIM card in for the country I'm going to however I haven't backed up my phone for ages because I don't have enough storage so when I put the new foreign sim in my phone will I loose all my apps and photos?

No. Doing things with the SIM has nothing to do with the content on the phone.

No you will not lose anything. But before putting a new sim, make sure your phone is unlocked to read foreign sims, because it won't work without it being unlocked. If you're on Verizon network now, then your phone comes unlocked. Yay!
If AT&T, then you can ask them to do it for you, or go to swiftunlocks.com and they will do it for you. I believe they also do T-Mobile, but it's a lot more expensive. As for sprint, you're out of luck unless sprint unlocks it for you.