<p>A variety of microstructures have been obtained in the TA15 alloy through multiple solution treatments and aging (STA). The volume fraction and size of the <i>α</i> lamellae (<i>α</i>_l phase) and secondary <i>α</i> nanoplates (<i>α</i>_s phase) were systematically controlled, and the intrinsic relationships among heat treatment parameters, microstructures, and mechanical properties were investigated in depth. The study reveals that slower cooling rate, higher aging temperature, and longer aging duration are conducive to the coarsening and increased volume fraction of the <i>α</i>_l phase. Conversely, increasing the cooling rate, widening the temperature difference between the solution and aging treatment, and extending the aging time result in a high volume fraction of the <i>α</i>_s phase. Mechanical properties results demonstrate that the strength of the alloy is primarily determined by the volume fraction of the <i>α</i>_s phase, and the ultimate tensile strength and yield strength can reach 1338 and 1127&#xa0;MPa, respectively, with the higher content and larger size of the <i>α</i>_s phase, respectively. However, the ductility is mainly influenced by the size of the <i>α</i>_l phase, where coarse <i>α</i>_l phase leads to a longer dislocation slip path, thereby enhancing ductility and resulting in an elongation of up to 19 pct. Furthermore, two strength prediction models have been established, which further proved that the improvement in the strength originates from the Orowan strengthening of the <i>α</i>_s phase and its interaction with dislocations. The strategy, which involves synergistically optimizing strength and ductility through the precise control of the microstructure <i>via</i> heat treatment, is equally applicable to other titanium alloys, providing a new pathway for the microstructural design of high-performance titanium alloys.</p>