When prostate cancer is near the prostate wall, is it likely to spread or is it slow growing?

Neither. The location, in this case, does not answer your questions. Aggressiveness, the risk of spread or speed of spread is best predicted by biopsy results. The gleason score, as read by an expert, gives this detail. Read here: http://1.Usa.Gov/m7kd5m. The psa value, the prostate exam, and the number of biopsies involved also help answer the question in early pc.
Spread can be. Local, correlated with perineural invasion; or distant, correlated with gl score, invasion to semves, and high psa. The prostate has a capsule, and I use the simple dcp or ece - (disease confined to prostate/extraprostatic extension). Growth rate is often measured by the rate that the psa doubles. Some cases are "watchable", others (psa >20; gl > 7) need treatment regardless.