In most cases a suspension on a bike that is going to be ridden on the road is more of a hindrance than a help as it adds weight, can affect handing, rob power, and add another degree of complication to the bicycle.

Running higher volume tyres at proper inflation pressure can do much to smooth out your ride and if the ride is better you will often go faster.

Am running some 20 by 1.35 Comets on my P20 road bike and at 100 psi they offer a very nice ride and get even better when the bike is loaded for touring.

The 20 by 1 3/8 Kendas on my R20 roll out fast, handle well, and do a nice shop of taking up road shocks.

Have noted that because I sit far more forward on the road version I am more sensitive to front tyre pressure while on the the more upright R20 the rear pressure is more critical as the front end is pretty light / unweighted when I am riding.

You can always run a slighty wider tyre in the rear to increase your comfort level as well.

On bikes with wheels smaller than 20 inches you are going to have to do more to deal with ride quality issues so having very good tyres will make a lot of differences and a well designed suspension is a beautiful thing but these are also very expensive.