Hornby's N15 does not have a lot of room in the loco for extra equipment, although some later models have a DCC socket in the
Ours came with an 8pin DCC socket up front, which we've removed, cut off the diagonal mount, and made room for a SugarCube
speaker. The Zimo MX648 decoder fits neatly into the remaining space at an angle, with motor and pickups wired simply.
Here is another example, with MX648 sound decoder and SugarCurve7 - a simple approach which fits in without any squeezing!