Don’t try to do i all at once! Start at the 1:15 you were given, and keep records of bg, carbs you ate, and dosing for a few days. You’ll probably begin to see patterns. If you’re consistently high at lunch, then nudge up your ratio for lunch. NUDGE is the key - don’t make any big changes. You can do this 
Hey Jess – adult diagnosed last Dec here. I am on 1:10 for breakfast and lunch, and 1:12 after. I am 125ish and 5’6 1/2" and thus have heard some snide remarks re my ratio (“you must be type 2!” said the not very bright dietician). But I am keeping very tight control; aiming for 120 1 hour after eating.
Re grazing vs meals, and “stacking” insulin – you’ll probably want to look into getting the pump; I find it allows WAAAY more meal flexibility. And one thing I learned on this site – correct me if I’m wrong, comrades – is that if your carb count is accurate, and if your ratios are correct, stacking insulin is not an issue with MEAL boluses. It’s only an issue with CORRECTION boluses. I have acted accordingly since learning that, and haven’t had a problem. My lows are exercise-induced, or bad-carb-count induced.
yeah, do you think that re the food packages? I’m starting to wonder if some are flat out LIES. Feh.
I’m still adjusting mine (T2 here, on MDI or “multiple daily injections”, not the pump). Currently a ratio of 1:4 seems to be working the best. I have quite a bit of insulin resistance. My doctor started me at 1:30 which was just ridiculous – I might as well have been injecting water. I agree with others that some of us need an I:C ratio that varies during the day. I tend to go a bit lower in the afternoons (79, 83), but I’m a bit higher after dinner/before bed (145, 160 – given the same foods and the same 1:4 ratio) so I may bump it up to 1:5 for late-morning snacks or lunch and cut back further on carbs at dinner.
I am actually higher in the morning so my ratio from midnight to 9:00 am is 1:9 and 1:12 the rest of the day, you have to find what works best for you according to your blood sugar patterns
My endo’s been trying to tweak mine, since my control isn’t very good but at the moment its 1:10.
It used to be 1:8, then 1:12, before that 1:15, and before that it was 1:20.