It's only a 1.8litre 8v (129bhp) so isn't that quick until you hot about 4500rpm. It has daft torque and power curves. They are low until about 3500rpm where they zoom up to max.
My Silverstone has max torque at about 5500rpm and mak power at about 6200rpm so you have to rev them to get the best.
Simple things to check/do:
Airfilter: Paper elements lose efficiency very quickly. Upgrade to a "sport" panel filter. DON'T use an induction kit...I have a bit off experience on the 155 with these.
Plugs: The car runs better with the OE Golden Lodge plugs. They cost about £20 for 8 and are 4 electrode jobbies.
Leads: My leads were brittle and old so I replaced them with Champion Triple Silicon things which made a difference to my car.
Is the car water temp getting to about 90ºC when warm ???
There are a few things which can lower the performance on that engine, but that's just a few to start with.
Also, does the car kinda "die" above 300rpm or when driving hard ??? That is another problem which is easy to check/fix, but I'll wait until I do another long post on how to fix it