multiple morningstar mppt in parallel?

Hi, I currently have 4x 135 watt panels and 2x Morningstar sunsaver MPPT controllers. These are installed on my boat. A pair of panels, wired in parallel for shade resistance is wired into each controller. I know this is slightly more wattage than morningstar recommends, but I talked with their tech support and they said it was close enough to not worry about it. They are currently networked together via a hub and I monitor them via MSView. I do see the controllers max out at 15A occasionally when conditions are perfect, but on a boat that is not too often.

My question is I have come into another 100 watts of panels I have room to install on the boat. Are there any major downsides with going with a third mppt 15A controller? I could always replace one of the two 15A with a 45, but that is more than 2x the price. If I would do that, would run the two 135's and two 50s in series since those are on my arch and not prone to shading, leaving the other two 135s in parallel on the 15A.

I know this solution is probably preferable, but I am also buying new batteries right now and am trying to save money for them as well.

Thoughts?