In recent years, the need to contain healthcare costs due to the growing public debt of many countries, combined with the need to reduce costly travel by patients unable to move autonomously, have captured the attention of public administrators towards tele-rehabilitation. This trend has been consolidated overwhelmingly following the Covid-19 pandemic, which has made it precarious, difficult and even dangerous for patients to access hospital facilities. We present a platform devoted to the rapid prototyping of Virtual Reality based, cognitive tele-rehabilitation exercises. Patients who experienced injury or pathology need to practice a continuous training in order to recover functional abilities, and the therapist need to monitor the outcomes of such practices. The Virtual Reality exercises are designed on Unity 3D to empower the therapist to set up personalised exercises in a easy way, enabling the patient to receive personalized stimuli, which are crucial for a positive outcome of the practice. Furthermore, the reaction speed of the system is of fundamental importance, as the temporal evolution of the scene must proceed parallel to the patient’s movements, to ensure an effective and efficient therapeutic response. So, we optimized the Virtual Reality application in order to make the loading phase and the startup phase as fast as possible and we have tested the results obtained with many devices: in particular computers and smartphones with different operating systems and hardware. The implemented platform integrates in Nu!Reha system®, a tele-rehabilitation set of services that helps patients to recover cognitive and functional capabilities.