The tips are just plastic and from the factory they were straight on the 150 and 152 but the "hoerner" tips of various designs are a very common modification at about 1 AMU installed (1 AMU = $1,000 regular dollars. Just part of the lies we tell ourselves about how much general aviation costs!) 😀
http://buyplaneparts.com/cessna-hoerner-high-performance-wing-tips-140a-150-170b-172-175-180-182-set/