New Meaco Arete 20L Dehumidifier, is the 55% smart setting realistic for our 1930s single skin brick house?

The original house is a 1937 single skin brick build, with an extension added on 15 years ago, the extension is considerably warmer as you'd expect. For the last year or so we've had problems with mold in the older part of the house and for the last couple of weeks, we've been using our son's older Dehumidifier with it set at 65% humidity. It has made a difference to how the house feels.

Today our new Meaco Arete 20L arrived, it's just sitting unused at the moment while we wait for the refrigerant to settle (the instructions say to allow 6 hours). I've read through the info provided and it states that ths 'smart setting' uses a target of 55% humidity, does this sound like a realistic humidity target for our older house?

Thanks for any info.