Minimum amount of physical activity for reduced mortality and extended life expectancy: a prospective cohort study.https://www.ncbi.nlm.nih.gov/pubmed/21846575/
Compared with individuals in the inactive group, those in the low-volume activity group, who exercised for an average of 92 min per week (95% CI 71-112) or 15 min a day (SD 1·8), had a 14% reduced risk of all-cause mortality (0·86, 0·81-0·91), and had a 3 year longer life expectancy. Every additional 15 min of daily exercise beyond the minimum amount of 15 min a day further reduced all-cause mortality by 4% (95% CI 2·5-7·0) and all-cancer mortality by 1% (0·3-4·5). These benefits were applicable to all age groups and both sexes, and to those with cardiovascular disease risks. Individuals who were inactive had a 17% (HR 1·17, 95% CI 1·10-1·24) increased risk of mortality compared with individuals in the low-volume group.

Potential benefits of exercise training 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2665984/

​Related to coronary heart disease risk factors
 Increases serum high-density lipoprotein cholesterol levels
 Reduces serum triglyceride and possibly low-density lipoprotein cholesterol levels
 Reduces indices of obesity
 Reduces arterial blood pressure
 Improves insulin sensitivity and glucose levels
 Improves endothelial function
 Helps with smoking cessation efforts
 Reduces psychological stress
Hematologic
 Decreases hematocrit and blood viscosity
 Expands blood plasma volume
 Increases red blood cell deformability and tissue-level perfusion
 Increases circulatory fibrinolytic activity
Other
 Increases coronary flow reserve
 Increases coronary collateral circulation
 Increases tolerance of ischemia
 Increases myocardial capillary density
 Increases ventricular fibrillation thresholds
 Reduces atherosclerosis
 Possibly increases epicardial coronary artery size
 Reduces major morbidity and mortality