\[ \boxed { 4\, \left ( y \left ( x \right ) \right ) ^{2}{\frac {{\rm d}^{3}}{{\rm d}{x}^{3}}}y \left ( x \right ) -18\,y \left ( x \right ) \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}y \left ( x \right ) +15\, \left ( {\frac {\rm d}{{\rm d}x}}y \left ( x \right ) \right ) ^{3}=0} \]
Mathematica: cpu = 0.075010 (sec), leaf count = 37 \[ \text {DSolve}\left [4 y(x)^2 y^{(3)}(x)+15 y'(x)^3-18 y(x) y'(x) y''(x)=0,y(x),x\right ] \]
Maple: cpu = 0.203 (sec), leaf count = 26 \[ \left \{ y \left ( x \right ) ={\frac {{\it \_C3}}{ \left ( -{{\it \_C2}} ^{2}-2\,{\it \_C2}\,x-{x}^{2}+4\,{\it \_C1} \right ) ^{2}}} \right \} \]