The height of my loft is approx 1.5metres. Is this too low for a loft conversion? What are the options?

1.5m from the top of the ceiling joist to the underside of the ridge board is too low to form a loft room.  The minimum measurement would be 2.1m, the only  option available is to raise the ridge and re pitch the roof at a steeper angle.  Obviously this would only be feasible on a detached property and would be subject to approval from your local planning department.