Robust, flexible, and high throughput are key features for future wireless Multi-Input Multi-Output (MIMO) communication system implementations. Furthermore, iterative processing is being widely investigated and proposed nowadays to cope with the increasing transmission quality requirement. However, these advanced techniques pose a real challenge in terms of complexity. A typical example in this domain is the significant performance improvement offered by the use of turbo equalization with turbo decoding for applications where the propagation channel experiences multipath effects. For this iterative system, and targeting a reduced complexity MIMO turbo receiver with high error correction feature for different modulation schemes and code rates, we analyze the impact of the demapper taking into account the a priori information (turbo demodulation) on the MIMO system complexity. We demonstrate that the adoption of turbo demodulation in this context can lead to significant complexity reduction for specific system configurations. Simulations show that applying feedback to the demapper reduces the overall number of iterations (thus arithmetic operations and memory accesses) for all modulations schemes except for QPSK. This reduction in number of iterations is obtained along with lower error rate performances. Results show a complexity reduction which can reach 24.5% in arithmetic operations and 31.8% in write access memory for QAM16 modulation scheme with 4x4 MIMO Spatial Multiplexing (SM) antenna.