Rabbi Eleazar HaKatan writes: "Recite the whole prayer service in order, but, as the rabbis say: 'Whether you do more or less, it is all the same, as long as your heart is turned to God' (Berachot 5)
A little prayer with your heart directed is better than much prayer without. (Tur)
If by shortening your prayers you have better concentration, it is better to shorten them, for little with devotion is better than much without. (The Kotsker Rebbe)