Every company has their SOP and policies. If your company allows you to be at 230kts at 1500 ft, then you are entitled to do so. But pilots in SIA and other established airlines are duty bound to comply with SOPs. Otherwise disciplinary action could be taken against them.
Again, ATC will determine the speeds to be flown if traffic is heavy. In many airports speed limits are imposed to manage traffic flow unless ATC determines otherwise for separation purposes. Yeah, I have done 250 kts on downwind in Chicago O'Hare on a B744, but that is becoz' ATC requires me to do so due to traffic separation.
Airmanship plays an important part as well. In airports where speed control is not mandatory, if one sights traffic ahead on their TCAS system or visually, one should adjust his speed accordingly to allow proper separation. If you are number one for approach, then by all means, keep up your speed (within SOPs and ATC's approval of course) to minimise delays.