I think that depends a lot on the master’s interface design. You might struggle with 15m and only a 4K7 pull-up. But before considering making the pull-up stronger you need to determine if it’s pulling to 3.3V or 5V (there’s a thread about that here). My conclusion further down in that thread was that it’s that 4K7 pull-up that’s protecting the 3.3V input from too much current from the 5V source.