No - on the contrary. 6 to 8 weeks is in some ways better than 3 to 4 weeks interval. The full process of collagen remodeling takes roughly 3 months. There is however no full concensus amongst experts on what the perfect interval is, but it is clear that collagen is not fully remodeled after 3 to 4 weeks. Some dermatologists use less than 3 weeks with a 1.5 mm roller and some use a month. If you want to be on the safest side possible and still have the full benefits of dermarolling, then your proposed interval is a good choice. The worst that can happen is that progress will be slower, but it is also possible that progress is just as fast, with, in the long term, even better results. It's not an exact science yet.
The problem we experienced is that our competitors have no interest in, or knowledge of microneedling and skin care. None of them, not a single dermaroller seller understands dermarolling. These people are 24 year old Hong Kong Chinese guys who became agents for a producer because they speak English. They recommend rolling twice a week with a 1.5 mm dermaroller not because it is a good idea, but because they want to sell many rollers - a roller blunts a little with every use so the more often you roll, the more money they make.
Do not trust anyone selling dermarollers, or endorsing a brand, or linking to dermarollers, or offering a dermarolling service etc. to tell you how often to roll!
We were initially not even believed by our own customers when we said that the best interval is around one month. We were inundated with incredulous questions. That's how harmful commercial propaganda can be, because it really is a bad idea to roll too often with long needles.
We are also commercial but we are in it for the long term. We want our customers to spread the word on how trustworthy we are in our advice, so that we will slowly but surely grow. The young Chinese guys are only interested in a quick buck. We don't need to - we both are pensioners and we never worry about money. So here, we'll try to get you real advice, not advice that yields us a few more sales.
So, whatever your reason you may have for a 6-8 week interval with 1.5 mm needles: No problem at all. If you want to be extra careful and you don't care about how long it takes to get results, but you want the best results achievable, go for a longer interval rather than shorter. Most customers are begging us to give them the goahead for shorter intervals..