Found these specs for them:
Scheme 3 ways, 3 speaker bass-reflex scheme, and a bookshelf type
Unit
For low-pass: 25cm cone type
For mid ranges: 12cm cone type
For high regions: 5cm horn type
Frequency characteristic 45Hz - 20000Hz
The maximum input 25W
Impedance 8ohms
Output sound pressure level 100dB/W
Cross over frequency 1500Hz, 5000Hz (12 dB/oct)
Dimensions Width 358x height 620x depth of 300mm
Weight 15.7kg


As you can see the maximum input is 25 watts and the rated SPL at 1 watt is 100. They will work great with the 2150 but I agree they need a sub for best performance and so you don't have to push them too hard. I would also suggest putting a half amp fuse in line with the positive speaker wire when you connect it to the amp. That way, a transient on the system doesn't damage your vintage speakers for which I am sure there are no parts available. You can go smaller than that but you might have to change the fuses occasionally when they blow.

As far as the sub, get a good powered sub and connect it to the 2150s sub out. If the sub does not have a bypass mode you just have to set the low pass filter setting all the way up and let the 2150 do the bass management. You won't believe the change in how the system sounds even with a cheap subwoofer. My first sub was a KLH 8 inch with 100W of power and it made a huge difference because the mains no longer had to work so hard at the low end. I would cross you mains over above 100 HZ and see how it sounds and then you can dial it in to your tastes.