335i is DIFFERENT
I have got to believe that the turbo engines should but put into a different category. Understanding the continued argument that BMW knows best and 15k oil changes are appropriate ~ I just can't help but believe that 230-250 oil temps beat up the oil.
Strong beliver in cheapest LL-01 oil at a min interval of 7.5K for BMW turbo engines with 7qt sump. SO, M1 0W-40 or BMW 5W-30 or GC --- any LL01 that you can find and stick with it.
Here is an Alabama Analogy:
If BMW built a pair of socks that could last for 15 months without wearing out ~ would you put on a pair and follow their instruction. A true Southerner would think that they may indeed last for 15 mo - but would certainly get dirty and need a wash / require changing (stink like hell).