As others say, the 15.5mph limit is a killer for commutes, after my hardtail died i’ve had to use my ebike once or twice a week to commute and it’s not saving any effort, the motor cuts in for uphills and maybe windy days into headwinds, so it’s weird that you are feeling effort on the easy bits, and no effort on the climbs, and still getting to work sweaty!
Wish they’d up the limit to 20mph, which seems sensible enough, and would cover commuters as well, i enjoy using my normal full susser more for commutes, but it’s got a nicer drivetrain and shocks, so loathe to using it for anything other than dry commutes sparingly.