FIFTEEN TO ONE AND ALL

Fifteen-letter words in fairly common use:

1 straightforward
2 appropriateness
3 electromagnetic
4 rationalisation
5 dessertspoonful
6 undistinguished
7 entrepreneurial
8 decontamination
9 individualistic
10 professionalism
11 distinguishable
12 unsophisticated
13 notwithstanding
14 unsubstantiated
15 misapprehension
16 comprehensively
17 dissatisfaction
18 experimentation
19 gastroenteritis
20 unwholesomeness
21 confidentiality
22 physiotherapist
23 contemperaneous
24 condescendingly
25 disrespectfully
26 resourcefulness
27 heterosexuality
28 intellectualise

Source: various