[tex]\qquad \qquad\huge \underline{\boxed{\sf ᴀɴsweʀ}}[/tex]
Yes ! The given lengths can be sides of a triangle
Because :
1. sum of any two sides is smaller than the third side
that is ;
[tex]\qquad \sf \dashrightarrow \: 6 + 15 > 20[/tex]
[tex]\qquad \sf \dashrightarrow \: 6 + 20 > 15[/tex]
[tex]\qquad \sf \dashrightarrow \: 20 + 15 > 6[/tex]
and
2. Difference of any two sides is smaller than the third side :
[tex]\qquad \sf \dashrightarrow \: 15 - 6 < 20[/tex]
[tex]\qquad \sf \dashrightarrow \: 20 - 6 < 15[/tex]
[tex]\qquad \sf \dashrightarrow \: 20 - 15 < 6[/tex]