Main speaker specs to consider
Short answer: yes you could use this speaker, but maybe you shouldn't.

Power Capacity

Simply put, RMS power capacity = safe power capacity.

Peak power ratings are the marketing departments' favorite, because peak power of even the smallest speakers can be up to 1000 Watts!!! (For one microsecond. Right before being engulfed in flames.) If you do not know how peak power rating is measured, it is a useless number.

"But wait, this speaker is 15W RMS, and my amp is 20W..."

Trust me, your amp will never output 20 Watts under usable circumstances. If you were to turn it all up, and somehow protection wouldn't kick in, your music will sound as if you're farting trough a megaphone. It sounds horrible, even if you're into dubstep.

All in all, based purely on power rating this speakers and amp will play nice together. Don't turn your amp up all the way, and it will use those 'spare watts' to give you a nice, dynamic output.

Maximum Excursion

This is how far the speaker cone (the moving part) can travel before irreversible damage occurs. It's what makes people upload movies of their subwoofer to Youtube. For your design, you should not worry about this.

Resonant Frequency

If you keep pushing a decent sized tree at just the right speed, and you will notice that your relatively low force is able to move the tree remarkably easy. This is because you keep adding force to the tree at it's resonance frequency.

The same goes for speakers. Now, it's no problem at all if the resonant frequency appears in output signal every once in a while, but it's not the best idea to constantly use a speaker near or at its resonant frequency. Simplified, the speaker could shake 'out of control', sounding bad and even damaging itself.

Frequency Range

As Naz already pointed out, the frequency range of this speakers is limited. Normally, it is described as the range between the two point where the sensitivity of the speaker (how well it can reproduce the frequencies) drops a relative 3dB. Here, - again, marketing - it is measured as the range between the 10dB drops in sensitivity.

So, could you use this speakers? Yes. Should you use this speakers? That is up to you. My advice is to look around for other (slightly bigger) loudspeakers, as this will probably improve the frequency range, especially towards the lower end. The magic words are 'fullrange driver' here. Do not expect earth rattling bass from your amplifier, however, when paired with the right speakers you will be able to produce a very nice sound.

Good luck!